It has become demanded to further improve various performances, such as heat resistance, mechanical properties, chemical properties, electrical properties, and reliability, in the electrical equipments developed in recent years, as compared to the conventional electrical equipments. Under the situations, excellent abrasion resistance, thermal aging resistance property, and solvent resistance have become required from insulated wires, such as enameled wires, that are used as magnet wires for electrical equipments for aerospace use, electrical equipments for aircraft, electrical equipments for nuclear power, electrical equipments for energy, and electrical equipments for automobiles. For example, in the recent years, for electrical equipments, it sometimes has been required to show an excellent thermal aging resistance over a long period of time of use.
On the other hand, in recent years, advance of the electrical equipment represented by motors or transformers, has been progressed resulting in size reduction and improved performance. Thus, it becomes usual in many cases that insulated wires are used in such a way that the insulated wires are processed by winding (coil processing) and they are pushed into a quite small space to pack. Specifically, it is no exaggeration to say that the performance of a rotator, such as a motor, is determined by how many wound wires produced by processing the insulated wires into a coil shape can be held in a stator slot. As a result, improvement of the ratio of the sectional area of conductors to the sectional area of the stator slot (space factor described below) has been required to be particularly highly increased.
For the reasons discussed above, it has been lately attempted to use a rectangular wire in which the conductor has a shape similar to a quadrilateral (square or rectangle), as a means for increasing the space factor. Use of a rectangular wire exhibits a dramatic effect in increasing the space factor. However, a corner portion of cross-section rectangular is extremely brittle to bending processing such as coil processing. Due to this, there is a problem that a coated film cracks when the rectangular wire is processed by applying strong pressure. In particular, it is known that the crack of the coated film tends to occur more easily as the curvature radius of the corner portion is smaller.
Further, regarding the insulated wire-processed coil which is used for a motor and the like, a response to a high electric current is sought in accordance with the high efficiency of the motor in recent years. Specifically, because an electric current is carried to a coil thereby raising the coil to high temperature, the above-described thermal aging resistance property is sought to the coil. Further, if embrittlement of the coil occurs due to vibration or the like, the embrittlement causes dielectric breakdown and therefore it is necessary to maintain flexibility and the like required as the coil which may be used even under a continuing heat environment.
Patent Literature 1 attempts to thicken an insulating film in order to solve a problem of the partial discharge and proposes to provide a thermoplastic resin having a low-relative permittivity as a coat resin on the outside of an enamel wire.
However, thickening of the insulating film decreases a space factor of the miniaturized equipment and therefore an adequate improvement is required.
Patent Literature 2 proposes to make the curvature radius of the insulating coat layer of the insulated wire smaller than a predetermined value in order to relax concentration of electric field which occurs when a corner portion of the insulated wire having an appropriately rectangular-shaped cross-section is adjoined to or comes into contact with a flat portion of an adjacent wire.
However, there is no description about the above-described thermal aging resistance property in Patent Literature 2.
Patent Literature 3 attempts to increase thickness of the insulating film of the rectangular wire in order to solve the problem of partial discharge. For example, it is proposed to coat a thermoplastic resin on an enameled rectangular wire. However, thickening of the insulating film decreases a space factor.